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    <script>

        // 短路赋值
        // a = a || 2;    // 参数默认值是2


        // function sum(a, b) {
        //     a = a || 0;
        //     b = b || 0;
        //     return a + b;
        // }


        // 函数的参数的默认值写法
        // function sum(a = 0, b = 0) {
        //     return a + b;
        // }

        // console.log(sum(1));




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